Vortex-type grit chamber

ABSTRACT

A grit removal unit including an influent channel directing wastewater with grit into a round grit removal chamber and an effluent channel receives wastewater output from the chamber. A divider wall extends upwardly between the sides of the influent channel, and gates at the upstream end of the divider wall are adjustable to selectively open channel portions on opposite sides of the divider wall. An output guide member is mounted to allow selective adjustment of output flow opening width “c” to the effluent channel. The output guide member has a horizontal bottom extending from the chamber into the effluent channel across the width of the output opening, and a guide wall extending upwardly from the guide member bottom. The guide wall has a forward end spaced from the chamber annular vertical wall to define the output flow opening width therebetween.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims the benefit of thefiling date of U.S. Provisional Ser. No. 61/723,935, filed Nov. 8, 2012,and U.S. Ser. No. 13/837,712, filed Mar. 15, 2013 and issuing on May 10,2016 as U.S. Pat. No. 9,334,178, which are hereby incorporated byreference in their entirety.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

MICROFICHE/COPYRIGHT REFERENCE

Not Applicable.

FIELD OF THE INVENTION

The present invention relates to water or waste water treatment systemsthat incorporate a grit removal system, and more particularly to a grittrap for a waste water system.

BACKGROUND OF THE INVENTION

In many industrial and municipal waste systems, wastewater which isladen with grit is pumped from a primary recovery device in the wastestream to a secondary device (e.g., a cyclone separator) which furtherconcentrates the grit. The stream may also pass through a third device(e.g., a screw conveyor) to further dry and concentrate the grit.

Grit removal systems such as grit extractors or grit traps have beenused in many waste systems to remove grit from the waste water prior topassing the water on to a recovery device of the system. For example,one advantageous apparatus includes flumes for injecting and extractingliquid tangentially relative to a round chamber, creating a circularflow stream which causes the grit to settle near the bottom center ofthe round chamber. That grit in the injected liquid is thus removed fromthe liquid stream and collected in the storage chamber for relativelyeasy removal. Such an apparatus is disclosed in U.S. Pat. No. 6,811,697B2.

U.S. Pat. Nos. 3,941,698, 4,107,038 and 4,767,532, 7,971,732 alsodisclose vortex-type grit extractor apparatuses. U.S. Pat. No.4,767,532, for example, discloses an apparatus for removing grit inwhich a grit storage chamber is provided beneath the center of the roundchamber of the grit removal system. A removable plate substantiallyaligned with the floor of the round chamber generally separates the twochambers, with a central opening through the plate permittingcommunication between the chambers. A cylindrical shaft is rotatablysupported on its upper end above the round chamber and extends downthrough the round chamber through the plate central opening. Liquid flowin the round chamber forces grit particles to settle toward the chamberfloor, where they are urged radially inwardly so as to drop through theplate central opening into the grit storage chamber. A multi-bladedpropeller is mounted on that shaft above the plate, and rotates with theshaft to assist in the liquid flow to move the grit toward the platecenter opening. A pipe also extends down through the cylindrical shaftinto the grit storage chamber, and a pump is provided on the upper endof the pipe to allow grit in the bottom of the storage chamber to beremoved by pumping up through the pipe.

The disclosures of all of these patents are also hereby fullyincorporated by reference.

Operation of such grit removal units depend on removal of grit from thewaste water as the water flows from the influent channel around theround chamber to an effluent channel.

Further, since the flow of wastewater with such grit is not constant oruniform, a wide range of low to high flow rates need to be accommodatedover the life of the unit. Given such a potential range of flow rates,in which the influent channel needs to be able to handle high flowrates, problems can be encountered with low flow rates. For example,when flow rates are encountered which are much lower than the designrate of the grit removal apparatus, the velocity of the influent channelis significantly reduced at such low flow rates and undesirablepremature settling of grit in the influent channel can occur. Where suchlow flow rates are encountered over a long period of time, this canresult in grit undesirably settling and remaining in the influentchannel for long periods of time, until a significant flow event occurswhich is capable of lifting and flushing the grit to the chamber forremoval,

The present invention is directed toward overcoming one or more of theproblems set forth above.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a grit removalunit for a wastewater system is provided, including a round grit removalchamber defined by a bottom surface and a substantially annular verticalwall extending up from the bottom surface, with input and outputopenings through the annular vertical wall. The input opening has abottom surface above the bottom surface of the grit removal chamber,with a sloped bottom surface extending between the input opening bottomsurface and the chamber bottom surface. The output opening has a bottomabove the bottom surface of the grit removal chamber. An influentchannel directs wastewater with grit into the chamber through theannular vertical wall input opening, and has two side walls includingone which is substantially tangential to the annular vertical wall. Adivider wall extends upwardly in the influent channel between theinfluent channel side walls and defines a first influent channel portionbetween the divider wall and the one influent channel side wall and asecond influent channel portion between the divider wall and the otherinfluent channel side wall. First and second gates are at the upstreamend of the first and second influent channel portions, respectively,with the first gate being adjustable to selectively open flow ofwastewater with grit to the first influent channel portion and thesecond gate being adjustable to selectively open flow of wastewater withgrit to the second influent channel portion. An effluent channelreceives wastewater output from the chamber through the output opening,and an output guide member is adjustably mounted to the chamber andeffluent channel whereby the output flow opening width may beselectively adjusted. The output guide member has a substantiallyhorizontal bottom extending from the chamber into the effluent channelacross the width of the output opening, and a guide wall extendingupwardly from the guide member bottom. The guide wall has a forward endspaced from the chamber annular vertical wall at the output opening todefine the output flow opening width therebetween, and a rear endextending through the output opening and into the effluent channel.

In one form of this aspect of the invention, adjustment of the first andsecond gates and the output guide member are coordinated based onanticipated flow through the grit removal unit.

In another form of this aspect of the invention, the second gate isclosed to block flow through the second influent channel portion whenlow flow of wastewater with grit is anticipated.

In still another form of this aspect of the present invention, theoutput opening is positioned at about 270 degrees around the round gritremoval chamber from the input opening. In a further form, the influentchannel and the effluent channel are substantially parallel with thewastewater flowing in opposite directions.

In yet another form of this aspect of the present invention, the dividerwall is spaced a distance “a” from the one influent channel side walland spaced a distance “b” from the other influent channel side wall,where “a” and “b” are not equal. In a further form, the distance “a”provides a flow velocity sufficiently high during anticipated periods oflow flow of the influent wastewater with grit to prevent significantsettlement of grit from the wastewater in the influent channel.

In another form of this aspect of the invention, the output guide memberis mounted whereby its opening angle “d” and the output flow opening “c”may be selectively adjusted.

In still another form of this aspect of the invention, the guide wall ofthe output guide member is selectively positioned relative to thechamber vertical wall to provide an effective effluent opening ofsubstantially the same width as width of the open influent channelportions.

In yet another form of this aspect of the invention, the divider wall isa baffle having an adjustable height.

In accordance with another aspect of the present invention, a gritremoval unit for a wastewater system is provided, including a round gritremoval chamber defined by a bottom surface and a substantially annularvertical wall extending up from the bottom surface, with input andoutput openings through the annular vertical wall. The input opening hasa bottom surface above the bottom surface of the grit removal chamber,with a sloped bottom surface extending between the input opening bottomsurface and the chamber bottom surface. The output opening has a bottomabove the bottom surface of the grit removal chamber. An influentchannel directs wastewater with grit into the chamber through theannular vertical wall input opening, and has two side walls includingone which is substantially tangential to the annular vertical wall. Adivider wall extends upwardly in the influent channel between theinfluent channel side walls and defines a first influent channel portionbetween the divider wall and the one influent channel side wall and asecond influent channel portion between the divider wall and the otherinfluent channel side wall. First and second gates are at the upstreamend of the first and second influent channel portions, respectively,with the first gate being adjustable to selectively open flow ofwastewater with grit to the first influent channel portion and thesecond gate being adjustable to selectively open flow of wastewater withgrit to the second influent channel portion. An effluent channelreceives wastewater output from the chamber through the output opening.

In one form of this aspect of the invention, the second gate is closedto block flow through the second influent channel portion when low flowof wastewater with grit is anticipated.

In another form of this aspect of the present invention, the outputopening is positioned at about 270 degrees around the round grit removalchamber from the input opening. In a further form, the influent channeland the effluent channel are substantially parallel with the wastewaterflowing in opposite directions.

In yet another form of this aspect of the present invention, the dividerwall is spaced a distance “a” from the one influent channel side walland spaced a distance “b” from the other influent channel side wall,where “a” and “b” are not equal. In a further form, the distance “a”provides a flow velocity sufficiently high during anticipated periods oflow flow of the influent wastewater with grit to prevent significantsettlement of grit from the wastewater in the influent channel.

In still another form of this aspect of the invention, the divider wallis a baffle having an adjustable height.

In accordance with still another aspect of the present invention, a gritremoval unit for a wastewater system is provided, including a round gritremoval chamber defined by a bottom surface and a substantially annularvertical wall extending up from the bottom surface, with input andoutput openings through the annular vertical wall. The input opening hasa bottom surface above the bottom surface of the grit removal chamber,with a sloped bottom surface extending between the input opening bottomsurface and the chamber bottom surface. The output opening has a bottomabove the bottom surface of the grit removal chamber. An influentchannel directs wastewater with grit into the chamber through theannular vertical wall input opening and has two side walls. An effluentchannel receives wastewater output from the chamber through the outputopening, and an output guide member is adjustably mounted to the chamberand effluent channel whereby the output flow opening width may beselectively adjusted. The output guide member has a substantiallyhorizontal bottom extending from the chamber into the effluent channelacross the width of the output opening, and a guide wall extendingupwardly from the guide member bottom. The guide wall has a forward endspaced from the chamber annular vertical wall at the output opening todefine the output flow opening width therebetween, and a rear endextending through the output opening and into the effluent channel.

In one form of this aspect of the invention, the output guide member ismounted whereby its opening angle “d” and the output flow opening “c”may be selectively adjusted.

In another form of this aspect of the invention, a divider wall extendsupwardly in the influent channel between the influent channel side wallsand defines a first influent channel portion between the divider walland the one influent channel side wall and a second influent channelportion between the divider wall and the other influent channel sidewall. First and second gates are at the upstream end of the first andsecond influent channel portions, respectively, with the first gatebeing adjustable to selectively open flow of wastewater with grit to thefirst influent channel portion and the second gate being adjustable toselectively open flow of wastewater with grit to the second influentchannel portion. In a further form, the divider wall is a baffle havingan adjustable height.

Other objects, features, and advantages of the invention will becomeapparent from a review of the entire specification, including theappended claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of the round chamber and influent and effluentchambers of a grit removal unit according to the present invention;

FIG. 2 is a side cross-sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a perspective view of the influent channel of the grit removalunit;

FIG. 3A is a partial perspective view of an alternate embodiment of theinfluent channel baffle having an adjustable portion;

FIG. 4 is a perspective view illustrating the output from the roundchamber to the effluent chamber; and

FIG. 5 is a perspective view of the round chamber and influent andeffluent channels of a grit removal unit according to the presentinvention; and

FIGS. 6a and 6b are top views of a portion of FIG. 1 showing alternateconfigurations of the influent channel gates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The advantageous features of a grit removal unit 10 according to thepresent invention are illustrated in the Figures.

Specifically, as is known in the art, the grit removal unit 10 includesa round chamber 12 having a bottom surface or floor 14 with a generallyannular vertical wall 16 extending upwardly from the floor 14.

Input and output openings 20, 22 through the annular vertical wall 16are connected to influent and effluent troughs or channels 30, 32, wherethe output opening 22 is raised above the floor 14 of the round chamber12. As illustrated, the output opening 22 may advantageously bepositioned at about 270 degrees around the round grit removal chamber 12from the input opening 20, although it should be understood that thepresent invention may also be advantageously used in systems where theoutput opening 22 is at other positions relative to the input opening20. Wastewater with grit is carried into the round chamber 12 throughthe influent channel 30, with grit removed in the round chamber 12 andwastewater from which grit has been removed carried from the roundchamber 12 via the effluent channel 32.

As illustrated in phantom in FIG. 1, and as generally known in the art(such as taught in U.S. Pat. No. 7,971,732), a grit removal chamber 36may be provided at the bottom of the round chamber 12 where grit andother objects may be directed and then removed. Not shown but as alsorecognized in the art, a drive including, for example, a multi-bladedpropeller, may also be provided to facilitate movement of grit removedfrom the wastewater toward and into the grit removal chamber 36.

In accordance with one aspect of the present invention, the influentchannel 30 is defined by a bottom 40 which is at a level slightly abovethe bottom surface 14 of the round chamber 12, and two upright sidewalls 42, 44, one of which 42 is substantially tangential to the annularvertical wall 16 of the round chamber as best seen in FIG. 1. The bottom40 of the influent channel 30 tapers down (at 48) to the level of theround chamber bottom surface 14 at the input opening 20 of the chamber12.

As best illustrated in FIGS. 2-3, a baffle or divider wall 50 extendsupwardly from the influent channel bottom 40 and is substantiallyparallel to the side walls 42, 44. The baffle 50 serves to effectivelydivide the influent channel 30 into separate smaller passages 54, 56.The baffle 50 may have an adjustable portion 52 (see FIG. 3A) suitablysecured along its top to allow the overall height of the baffle to beadjusted if and as desired. Such adjustability allows the unit 10 tocompensate for variations in the influent flow volume introduced intothe influent channel as well as meeting actual site conditions. Further,the adjustable portion 52 may be advantageously designed to allowinfluent flow volumes in excess of the flow condition to overflow thedivider wall to maintain the desired velocity in each of the influentchannel passages 54, 56 and not cause an excess flow velocity to occurin either channel passage 54, 56.

The baffle 50 is spaced a distance “a” from the outer influent channelside wall 42 and a distance “b” from the inner influent channel sidewall 44 (see FIG. 1). While “a” and “b” may advantageously be differentdistances so that the separate smaller passages 54, 56 are differentsizes, it should be understood that at least some advantages of thepresent invention could be obtained where “a” and “b” are equal. Itshould also be appreciated that the distance “a” may be selected so asto provide a sufficiently higher flow velocity during anticipatedperiods of low flow of the influent wastewater to prevent significantgrit settlement in the influent channel 30.

Gates 60, 62 are provided at the upstream end of the baffle 50, whichgates 60, 62 may be selectively opened and/or closed to allow flowthrough either or both of the separate passages. As illustrated, thegates 60, 62 include handles 64, 66 allowing an operator to manuallygrasp the gates 60, 62 by the handles 64, 66 and raise or lower (orremove or install) the gates 60, 62 to open or close selected passages54, 56 on opposite sides of the baffle 50. As illustrated, the gates 60,62 each have a slide connection allowing vertical movement. It should beappreciated, however, that it would be within the scope of at least someaspects of the invention for the gates 60, 62 to also be supported in adifferent fashion to open and close each of the smaller passages 54, 56including, for example, pivoting movement around horizontal axes and/oraround vertical axes. Further, movement of the gates 60, 62 couldalternatively be controlled by powered drives (e.g., mechanically) whichcould be controlled manually or automatically based on flow ratemeasurements. Still further, whereas the gates 60, 62 as illustrated inthe Figures are perpendicular to the direction of wastewater flow (seeparticularly FIG. 3), at least some advantageous aspects of the presentinvention could be had with the gates 60, 62 oriented differently. (Forexample, the two gates 60, 62 could form a “V” shape when viewed fromabove, with the point of the “V” either facing the influent flow asillustrated by gates 60′, 62′ in FIG. 6a or oriented toward the inputopening 20 of the round chamber ) 12 as illustrated by gates 60, 62″ inFIG. 6b . Moreover, at least some aspects of the present invention couldbe had with gates 60, 62 which have a non-planar face, and/or a facewhich is not fully vertical.

For example, as illustrated in FIG. 3, one gate 60 may be opened and theother gate 62 closed during a low flow period to allow flow ofwastewater with grit through only the outer passage 54, thereby causingflow velocity to be increased over what it would be through bothpassages 54, 56 combined and decrease or eliminate undesirable settlingof grit onto the bottom of the influent channel 30 which would occur atsuch a lower flow velocity.

Where “a” is not equal to “b” as previously noted, it should beappreciated that each of the passages 54, 56 would be different, suchthat effectively three different effective influent channels 30 could beprovided, that is, passage 54 only, passage 56 only, and passages 54 and56 combined. During operation during which only one passage is opened,however, it should be appreciated that the outer passage 54 could beadvantageous in that it would provide a longer grit travel path, as wellas directing flow tangentially into the round chamber 12, and therebyincrease the probability of grit capture in the round chamber 12 asdesired.

At higher (e.g., normal design) flow rates, where flow velocity throughonly one passage (e.g., outer passage 54 as illustrated in FIG. 3) wouldbe too high to allow for proper grit removal in the round chamber 12),then both gates 60, 62 could be opened whereby the two passages 54, 56together would allow wastewater flow at the desired flow velocity (lowerthan would occur with just one passage 54 or 56 open).

It should be appreciated that though in the illustrated embodiment asingle baffle 50 with two gates 60, 62 are shown, it would be within thescope of at least some aspects of the present invention to provide morebaffles and gates. For example, two baffles and three gates could beprovided in the influent channel 30, in which case seven differenteffective influent flow channels could be presented (each of the threedifferent passages A, B, C alone, three different combinations of twopassages AB, AC, BC, and all three passages ABC). Typically, however, itwould be advantageous to open the passages sequentially beginning withthe outer passage (i.e., A, then AB with higher flow rates, then ABCwith still higher flow rates). Still further, one smaller passage couldbe provided with no gate such that flow through at least that onepassage would always be permitted.

An output baffle or guide member 70 is located at the output opening 22(i.e., the entrance to the effluent channel 32 from the round chamber12). The output baffle 70 includes a substantially horizontal bottom 74extending from the round chamber 12 into the effluent channel 32 acrossthe width of the output opening 22, and a guide wall 76 extendingupwardly (e.g., at a 90 degree angle) from the guide member bottom 74.The forward end 80 (see FIG. 1) of the guide wall 76 is spaced from thechamber annular vertical wall 16 at the output opening 22 to define anoutput flow opening width therebetween. The rear end 82 (see FIG. 1) ofthe guide wall 76 extends through the output opening 22 and into theeffluent channel 32, whereby wastewater which passes between the forwardend 80 of the guide wall 76 and the annular vertical wall 16 above theguide member bottom 74 will be directed into the effluent channel 32away from the round chamber 12.

The output baffle 70 advantageously limits short circuiting of grit fromthe influent channel 30 to the effluent channel 32 or from the floor 14of the chamber 12 near the effluent channel 32, with the guide wall 76acting to restrict the effective effluent channel opening area in orderto control velocity, and direct flow into the effluent trough, all ofwhich aids grit removal by helping to ensure that wastewater exiting viathe effluent channel 32 will have sufficient grit removed bysufficiently flowing through the round chamber 12 prior to reaching theeffluent channel 32.

Further, the output baffle 70 may advantageously be adjustably mountedrelative to the effluent channel 32 (allowing, e.g., horizontaltranslation and/or rotation about a vertical axis). Such adjustment maybe accomplished by, for example, manual or automatic operations. Forexample, the output baffle 70 can be mounted using a hinge, andhydraulic or electric operators can be mounted to the baffle 70 tochange its position. Moreover, control of such operators mayadvantageously be initiated by an operator by using simple switches, orcan be tied into additional instrumentation, such as the plantflowmeter, with adjustment of the baffle 70 being automatic based ondata input and logic control.

Adjustable mounting of the output baffle 70 allows selective adjustmentof the output flow opening width or effective effluent opening “c” (seeFIG. 1), as well as adjustment to both the opening angle “d” and theprotrusion distance “e” into the chamber 12 parallel to the influentflow. The adjustable opening angle “d” allows for better control ofeffluent velocity, and the output flow opening width “c” assists indeterring short circuiting at given opening angles.

Advantageously, the output baffle 70 may be positioned so that theeffective effluent opening “c” is the same width as the total influentchannel 30, and the protrusion distance “e” is such that the guide wall76 meets the side wall of the effluent channel 32 that is nearest theinfluent channel 30. While in normal operation the grit removal unit 10may not require adjustment to the opening angle or protrusion distanceon a regular basis, at full flow further opening the effluent channel 32via the opening angle “d” and/or protrusion distance “e” may beadvantageous. Moreover, at even lower flow, further closing the effluentchannel 32 via the opening angle “d” and/or protrusion distance “e” maybe beneficial to the performance.

It should be appreciated that grit removal units 10 according to thepresent invention may advantageously ensure proper operation of the unitto remove grit over the varying conditions which will be encounteredover the years long life of the unit.

The invention claimed is:
 1. A grit removal unit for a wastewatersystem, comprising: a round grit removal chamber defined by a bottomsurface and a substantially annular vertical wall extending up from saidbottom surface; a wastewater output from said grit removal chamber; awastewater input opening through said annular vertical wall, said inputopening having a bottom above the bottom surface of the grit removalchamber; an influent channel for directing wastewater with grit intosaid grit removal chamber through said input opening, said influentchannel having a bottom wall aligned with said input opening bottom, twoside walls extending up from said channel bottom wall with one of saidside walls substantially tangential to said annular vertical wall, andthe other of said side walls having a downstream end intersecting withsaid grit removal chamber annular vertical wall at said input opening,and a divider wall extending upwardly in said influent channel betweensaid influent channel side walls and having an upstream end and adownstream end, said downstream end terminating substantially inalignment with the downstream end of the other of said side walls ofsaid influent channel, wherein said divider wall and said influentchannel side walls are substantially parallel, and define a firstinfluent channel portion between said divider wall and said one influentchannel side wall and define a second influent channel portion betweensaid divider wall and said other influent channel side wall, said firstand second influent channel portions each having an upstream end and adownstream end; a transitional bottom surface sloped downwardly fromsaid influent channel opening bottom wall beginning at the alignment ofthe downstream ends of said divider wall and said channel other sidewall and extending toward said grit removal chamber bottom surfacewithin said grit removal chamber; and a first gate at the upstream endof one of said first and second influent channel portions, said firstgate being adjustable to selectively open or block flow of wastewaterwith grit to said first influent channel portion.
 2. The grit removalunit of claim 1, wherein said first gate is oriented in a firstsubstantially vertical plane, and further comprising a second gateoriented in substantially a second substantially vertical plane.
 3. Thegrit removal unit of claim 2, wherein said first and secondsubstantially vertical planes are substantially the same plane.
 4. Thegrit removal unit of claim 1, said wastewater output comprising aneffluent channel for wastewater output from said grit removal chamberthrough an output opening in said grit removal chamber, said outputopening having a bottom above the bottom surface of the grit removalchamber.
 5. The grit removal unit of claim 1, further comprising asecond gate at the upstream end of the other of said first and secondinfluent channel portions, said second gate being adjustable toselectively allow flow of wastewater with grit to said other influentchannel portion.
 6. The grit removal unit of claim 5, wherein saidsecond gate is closed to block flow through the other of said first andsecond influent channel portions when low flow of wastewater with gritis anticipated.
 7. The grit removal unit of claim 1, wherein saiddivider wall is spaced a distance “a” from said one influent channelside wall and spaced a distance “b” from said other influent channelside wall, where “a” and “b” are not equal.
 8. The grit removal unit ofclaim 7, wherein the distance “a” provides a flow velocity sufficientlyhigh during anticipated low flow of said wastewater with grit to preventsignificant settlement of grit from the wastewater in the influentchannel.
 9. The grit removal unit of claim 1, wherein said divider wallis a baffle having an adjustable height.
 10. The grit removal unit ofclaim 1, wherein said influent channel bottom wall is substantiallyhorizontal.
 11. A grit removal unit for a wastewater system comprising:a round grit removal chamber defined by a bottom surface and asubstantially annular vertical wall extending up from said bottomsurface; a wastewater output from said grit removal chamber; awastewater input opening through said annular vertical wall, said inputopening having a bottom above the bottom surface of the grit removalchamber; an influent channel for directing wastewater with grit intosaid grit removal chamber through said input opening, said influentchannel having a bottom wall aligned with said input opening bottom, twoside walls extending up from said channel bottom wall with one of saidside walls substantially tangential to said annular vertical wall, andthe other of said side walls having a downstream end intersecting withsaid grit removable chamber annular vertical wall at said input opening,and a divider wall extending upwardly in said influent channel betweensaid influent channel side walls and having an upstream end and adownstream end, said downstream end terminating substantially inalignment with the downstream end of the other of said side walls ofsaid influent channel, wherein said divider wall and said influentchannel side walls are substantially parallel, and define a firstinfluent channel portion between said divider a and said one influentchannel side wall and define a second influent channel portion betweensaid divider wall and said other influent channel side wall, said firstand influent channel portions each having an upstream end and adownstream end, a transitional bottom surface sloped downwardly fromsaid influent channel opening bottom wall beginning at the alignment ofthe downstream ends of said divider wall and said channel other sidewall and extending toward said grit removal chamber bottom surfacewithin said grit removal chamber, a first gate at the upstream end ofone of said first and second influent channel portions and oriented in afirst substantially vertical plane, said first gate being adjustable toselectively open or block flow of wastewater with grit to said firstinfluent channel portion; and a second gate oriented in substantially asecond substantially vertical plane; wherein said first and secondvertical planes intersect at an angle at the upstream end of the dividerwall, said first and second substantially vertical planes being at equalangles relative to said divider wall, where said equal angles are not 90degrees.
 12. A grit removal unit for a wastewater system, comprising: agrit removal chamber defined by a bottom surface and a substantiallyannular vertical wall extending up from said bottom surface; an inputopening through said annular vertical wall, said input opening having abottom above the bottom surface of the grit removal chamber; an outputopening through said annular vertical wall, said output opening having abottom above the bottom surface of the grit removal chamber; an influentchannel for directing wastewater with grit into said grit removalchamber through said input opening, said influent channel having asubstantially horizontal bottom surface between two substantiallyparallel side walls, wherein one of said side walls is substantiallytangential to said annular vertical wall and the other of said sidewalls intersects said annular vertical wall on a side of the inputopening; a divider wall extending upwardly from said influent channelbottom surface between and substantially parallel to said influentchannel side walls, said divider wall defining a first influent channelportion between said divider wall and said one influent channel sidewall and a second influent channel portion between said divider wall andthe other influent channel side wall, said divider wall having adownstream end substantially aligned with the intersection of the otherinfluent channel side wall with said annular vertical wall and saidfirst and second influent channel each having an upstream end and adownstream end; a transitional sloped bottom surface sloped downwardlyfrom said influent channel bottom surface from said divider walldownstream end toward said input opening; and a first gate at theupstream end of one of said first and second influent channel portions,said first gate being adjustable to selectively open or block flow ofwastewater with grit to said first influent channel portion.
 13. Thegrit removal unit of claim 12, further comprising a second gate at theupstream end of the other of said first and second influent channelportions, said second gate being adjustable to selectively open or blockflow of wastewater with grit to said other influent channel portion. 14.The grit removal unit of claim 13, wherein said second gate is closed toblock flow through said second influent channel portion when low flow ofwastewater with grit is anticipated.
 15. The grit removal unit of claim12, wherein said divider wall is spaced a distance “a” from said oneinfluent channel side wall and spaced a distance “b” from said otherinfluent channel side wall, where “a” and “b” are not equal.
 16. Thegrit removal unit of claim 15, wherein the distance “a” provides a flowvelocity sufficiently high during anticipated low flow of saidwastewater with grit to prevent significant settlement of grit from thewastewater in the influent channel.
 17. A grit removal unit for awastewater system, comprising: a grit removal chamber defined by abottom surface and a substantially annular vertical wall extending upfrom said bottom surface; an input opening through said annular verticalwall, said input opening having a bottom surface above the bottomsurface of the grit removal chamber, with a sloped bottom surfaceextending between said input opening bottom surface and said gritremoval chamber bottom surface; an output opening through said annularvertical wall, said output opening having a bottom above the bottomsurface of the grit removal chamber; an influent channel for directingwastewater with grit into said grit removal chamber through said annularvertical wall input opening, said influent channel having asubstantially horizontal bottom surface between two side wallssubstantially parallel to each other with one of said side wallssubstantially tangential to said annular vertical wall at one side ofsaid input opening and the other of said side walls having a downstreamend terminating at the other side of the input opening; a divider wallextending upwardly in said influent channel between and substantiallyparallel to said influent channel side walls and defining a firstinfluent channel portion between said divider wall and said one influentchannel side wall, said divider wall having upstream and downstream endswith its downstream end substantially aligned with the downstream end ofthe other of said side walls, and a second influent channel portionbetween said divider wall and said other influent channel side wall,wherein said first and second influent channel portions each include anupstream end adjacent the upstream end of the divider wall; first andsecond gates at the upstream end of said first and second influentchannel portions, respectively, said first gate being adjustable toselectively open flow of wastewater with grit to said first influentchannel portion and said second gate being adjustable to selectivelyopen flow of wastewater with grit to said second influent channelportion; a transitional bottom surface sloped downwardly from saidinfluent channel opening bottom surface beginning at the alignment ofthe downstream ends of said divider wall and said channel other sidewall and extending to said grit removal chamber bottom surface withinsaid grit removal chamber; and an effluent channel for wastewater outputfrom said grit removal chamber through said output opening.
 18. The gritremoval unit of claim 17, wherein: said first and second gates are eachsubstantially planar and substantially vertical with one side adjacentthe upstream end of the divider wall; said first gate other side beingsubstantially adjacent said one influent channel side wall; and saidsecond gate other side being substantially adjacent said other influentchannel side wall.
 19. The grit removal unit of claim 17, wherein saiddivider wall is spaced a distance “a” from said one influent channelside wall and spaced a distance “b” from said other influent channelside wall, where “a” and “b” are not equal.
 20. The grit removal unit ofclaim 19, wherein the distance “a” provides a flow velocity sufficientlyhigh during anticipated low flow of said wastewater with grit to preventsignificant settlement of grit from the wastewater in the influentchannel.